Nuclear export signal of IkappaBalpha interferes with the Rev-dependent posttranscriptional regulation of human immunodeficiency virus type I

Multiple Inhibitory Factors Act in the Late Phase of HIV-1 Replication: a Systematic Review of the Literature

The use of lentiviral vectors for therapeutic purposes has shown promising results in clinical trials. The ability to produce a clinical-grade vector at high yields remains a critical issue. One possible obstacle could be cellular factors known to inhibit human immunodeficiency virus (HIV). To date, five HIV restriction factors have been identified, although it is likely that more factors are involved in the complex HIV-cell interaction. Inhibitory factors that have an adverse effect but do not abolish virus production are much less well described. Therefore, a gap exists in the knowledge of inhibitory factors acting late in the HIV life cycle (from transcription to infection of a new cell), which are relevant to the lentiviral vector production process. The objective was to review the HIV literature to identify cellular factors previously implicated as inhibitors of the late stages of lentivirus production. A search for publications was conducted on MEDLINE via the PubMed interface, using the keyword sequence "HIV restriction factor" or "HIV restriction" or "inhibit HIV" or "repress HIV" or "restrict HIV" or "suppress HIV" or "block HIV," with a publication date up to 31 December 2016. Cited papers from the identified records were investigated, and additional database searches were performed. A total of 260 candidate inhibitory factors were identified. These factors have been identified in the literature as having a negative impact on HIV replication. This study identified hundreds of candidate inhibitory factors for which the impact of modulating their expression in lentiviral vector production could be beneficial.

NF-κB Signaling is Involved in the Effects of Intranasally Engrafted Human Neural Stem Cells on Neurofunctional Improvements in Neonatal Rat Hypoxic-Ischemic Encephalopathy

AIM

Hypoxic-ischemic encephalopathy (HIE) is a common neurological disease in infants with persistent neurobehavioral impairments. Studies found that neural stem cell (NSC) therapy benefits HIE rats; however, the mechanisms underlying are still unclear. The current study investigated the efficacy and molecular events of human embryonic neural stem cells (hNSCs) in neonatal hypoxic-ischemic (HI) rats.

METHODS

PKH-26-labeled hNSCs were intranasally delivered to P7 Sprague Dawley rats 24 h after HI. Neurobehavioral tests were performed at the indicated time after delivery: righting reflex and gait testing at D1, 3, 5, and 7; grid walking at D7 and 14; social choice test (SCT) at D28; and Morris water maze from D35 to 40. Protein expression was determined by Western blot analysis. Brain damage was assessed by cresyl violet staining and MBP staining. hNSC distribution and differentiation were observed by in vivo bioluminescence imaging and immunofluorescence staining.

RESULTS

(1) hNSCs migrated extensively into brain areas within 24 h after the delivery, survived even at D42 with the majority in ipsi-hemisphere, and could be co-labeled with NeuN or GFAP. (2) hNSCs reduced the upregulation in cytosolic IL-1β, p-IκBα, and NF-κB p65 levels, whereas enhanced nuclear p65 expression in HI rats at D3 after the delivery. (3) hNSCs decreased HI-induced brain tissue loss and white matter injury at D42 after the delivery. (4) hNSCs improved neurological outcomes in HI rats in the tests of righting reflex (within 3 days), gait (D5), grid (D7), SCT (D28), and water maze (D42).

CONCLUSION

Intranasal delivery of hNSCs could prevent HI-induced brain injury and improve neurobehavioral outcomes in neonatal HI rats, which is possibly related to the modulation of NF-κB signaling.

HIV persistence: chemokines and their signalling pathways

Latently infected resting CD4+ T cells are the major barrier to curing HIV. We have recently demonstrated that chemokines, which bind to the chemokine receptors CCR7, CXCR3 and CCR6, facilitate efficient HIV nuclear localisation and integration in resting CD4+ T cells, leading to latency. As latently infected cells are enriched in lymphoid tissues, where chemokines are highly concentrated, this may provide a mechanism for the generation of latently infected cells in vivo. Here we review the role of chemokines in HIV persistence; the main signalling pathways that are involved; and how these pathways may be exploited to develop novel strategies to reduce or eliminate latently infected cells.

Understanding HIV-1 latency provides clues for the eradication of long-term reservoirs

HIV-1 can infect both activated and resting, non-dividing cells, following which the viral genome can be permanently integrated into a host cell chromosome. Latent HIV-1 reservoirs are established early during primary infection and constitute a major barrier to eradication, even in the presence of highly active antiretroviral therapy. This Review analyses the molecular mechanisms that are necessary for the establishment of HIV-1 latency and their relationships with different cellular and anatomical reservoirs, and discusses the current treatment strategies for targeting viral persistence in reservoirs, their main limitations and future perspectives.

Nuclear translocation of TSC-22 (TGF-beta-stimulated clone-22) concomitant with apoptosis: TSC-22 as a putative transcriptional regulator

We examined the alteration of the subcellular localization of TSC-22 (TGF-beta-stimulated clone-22) after induction of apoptosis and the transcription-regulatory activity of TSC-22. In the living cells, TSC-22-green fluorescent protein (GFP) fusion protein was clearly localized to the cytoplasm, however, in the apoptotic cells, the TSC-22-GFP fusion protein was translocated from the cytoplasm to the nucleus. TSC-22 fused to GAL4-DNA binding domain (GAL4BD) did not show the transcriptional activity on the reporter genes in yeast and in HSG (salivary gland cancer cells) and Hela. However, in CHO cells, TSC-22-GAL4BD fusion protein strongly activated the reporter gene. The transcriptional activity of the leucine zipper structure of TSC-22 is greater than that of the full-length TSC-22. These findings suggest that after receiving the apoptotic stimuli, TSC-22 translocates from the cytoplasm to the nucleus and shows the transcription-regulatory activity.

IkappaBalpha and IkappaBalpha /NF-kappa B complexes are retained in the cytoplasm through interaction with a novel partner, RasGAP SH3-binding protein 2

IkappaBalpha inhibits the transcriptional activity of NF-kappaB both in the cytoplasm by preventing the nuclear translocation of NF-kappaB and in the nucleus where it dissociates NF-kappaB from DNA and transports it back to the cytoplasm. Cytoplasmic localization of inactive NF-kappaB/IkappaBalpha complexes is controlled by mutual masking of nuclear import sequences of NF-kappaB p65 and IkappaBalpha and active CRM1-mediated nuclear export. Here, we describe an additional mechanism accounting for the cytoplasmic anchoring of IkappaBalpha or NF-kappaB/IkappaBalpha complexes. The N-terminal domain of IkappaBalpha contains a sequence responsible for the cytoplasmic retention of IkappaBalpha that is specifically recognized by G3BP2, a cytoplasmic protein that interacts with both IkappaBalpha and IkappaBalpha/NF-kappaB complexes. G3BP2 is composed of an N-terminal domain homologous to the NTF2 protein, followed by an acidic domain sufficient for the interaction with the IkappaBalpha cytoplasmic retention sequence, a region containing five PXXP motifs and a C-terminal domain containing RNA-binding motifs. Overexpression of G3BP2 directly promotes retention of IkappaBalpha in the cytoplasm, indicating that subcellular distribution of IkappaBalpha and NF-kappaB/IkappaBalpha complexes likely results from a equilibrium between nuclear import, nuclear export, and cytoplasmic retention. The molecular organization of G3BP2 suggests that this putative scaffold protein might connect the NF-kappaB signal transduction cascade with cellular functions such as nuclear transport or RNA metabolism.

Human T-cell leukemia virus type 1 Tax shuttles between functionally discrete subcellular targets

Human T-cell leukemia virus type 1 (HTLV-1) Tax is a nuclear protein with striking pleiotropic functionality. We recently demonstrated that Tax localizes to a multicomponent nuclear speckled structure (Tax speckled structure [TSS]). Here, we examine these structures further and identify a partial overlap of TSS with transcription hot spots. We used a strategy of directed expression via fusion proteins to determine if these transcription sites are the subtargets within TSS required for Tax function. When fused to human immunodeficiency virus type 1 (HIV-1) Tat, the resulting Tat-Tax fusion protein displayed neither a Tat-like nor a Tax-like pattern but rather was targeted specifically to the transcription subsites. The Tat-Tax fusion was able to activate both the HIV-1 long terminal repeat (LTR) and the HTVL-1 LTR at the same level as the individual component; thus, targeting proteins to transcription hot spots was compatible with both Tax and Tat transcription function. In contrast, the fusion with HIV-1 Rev, Rev-Tax, resulted in a pattern of expression that was largely Rev-like (nucleolar and cytoplasmic). The reduced localization of Rev-Tax to transcription sites was reflected in a 10-fold drop in activation of the HTLV-1 LTR. However, there was no loss in the ability of Tax to activate via NF-kappaB. Thus, NF-kappaB-dependent Tax function does not require targeting of Tax to these transcription sites and suggests that activation via NF-kappaB is a cytoplasmic function. Selective mutation of the nuclear localization signal site in the Rev portion resulted in retargeting of Rev-Tax to TSS and subsequent restoration of transcription function, demonstrating that inappropriate localization preceded loss of function. Mutation of the nuclear export signal site in the Rev portion had no effect on transcription, although the relative amount of Rev-Tax in the cytoplasm was reduced. Finally, in explaining how Tax can occupy multiple subcellular sites, we show that Tax shuttles from the nucleus to the cytoplasm in a heterokaryon fusion assay. Thus, pleiotropic functionality by Tax is regulatable via shuttling between discrete subcellular compartments.

High-level replication of human immunodeficiency virus in thymocytes requires NF-kappaB activation through interaction with thymic epithelial cells

We have previously demonstrated that interaction of infected thymocytes with autologous thymic epithelial cells (TEC) is a prerequisite for a high level of human immunodeficiency virus type 1 (HIV-1) replication in thymocytes (M. Rothe, L. Chêne, M. Nugeyre, F. Barré-Sinoussi, and N. Israël, J. Virol. 72:5852-5861, 1998). We report here that this activation of HIV replication takes place at the transcriptional level through activation of the Rel/NF-kappaB transcription factors. We first demonstrate that an HIV-1 provirus (SF-2 strain) very effectively replicates in thymocytes cocultured with TEC whereas this provirus, with kappaB sites deleted, fails to replicate. We provide evidence that several NF-kappaB complexes are constitutively found in the nuclei of thymocytes either freshly isolated from the thymus or maintained in coculture with autologous or heterologous TEC. The prevalent complex is the heterodimer p50-p65. NF-kappaB activity is tightly correlated with the transcriptional activity of a long terminal repeat (LTR) of HIV-1 transfected in thymocytes. The cotransfection of this LTR with a mutated IkappaBalpha molecule formally demonstrates that LTR transactivation is regulated by members of the Rel/NF-kappaB family in thymocytes. We also showed that tumor necrosis factor (TNF) and to a lesser extent interleukin-1 (IL-1), secreted within the coculture, induce NF-kappaB activity and a correlative LTR transactivation. However IL-7, a crucial factor for thymopoiesis that is secreted mainly by TEC, is a necessary cofactor for NF-kappaB activation elicited by TNF or IL-1. Together, these data indicate that NF-kappaB activation, required for a high level of HIV replication in thymocytes, is regulated in a specific manner in the thymic microenvironment which provides the necessary cytokines: TNF, IL-1, and IL-7.

A role for RNA helicase A in post-transcriptional regulation of HIV type 1

Retroviruses must bypass the tight coupling of splicing and nuclear export of mRNA in their replication cycle because unspliced genomic RNA and incompletely spliced mRNA must be exported to the cytoplasm for packaging or translation. This process is mediated by a cis-acting constitutive transport element (CTE) for simple retroviruses and by the trans-acting viral protein Rev in concert with its response element (RRE) for complex retroviruses (e.g., HIV). Recently, we identified RNA helicase A (RHA) as a potential cellular cofactor for CTE. Here, we report that RHA also plays a role in Rev/RRE-mediated gene expression and HIV replication. RHA binds weakly to HIV-1 RRE independently of Rev. Overexpression of RHA, but not of an RHA mutant lacking helicase activity, increased both Rev/RRE- and CTE-dependent gene expression and the levels of unspliced HIV mRNA. Microinjection of antibodies to RHA into nuclei dramatically inhibited both CTE- and Rev-dependent gene expression in human cells. Exogenous RHA cDNA, but not the mutant RHA, rescued this inhibition. We propose that RHA is required to release both CTE- and RRE-containing mRNA from spliceosomes before completion of splicing, thus freeing them for nuclear export.